Fluorocarbons (CFCs) have conventionally been the main refrigerant used in refrigeration devices; however, developments have been made over the past several years in regard to technologies in which carbon dioxide is used as a refrigerant. Carbon dioxide refrigeration cycles, such as disclosed in Japanese Laid-open Patent Publication No. 2001-74342, are widely known in the field of air conditioners used in automotive vehicles, and commercial products in which carbon dioxide is used as a refrigerant are used in the field of hot-water-supplying devices.